Drop support for older Barback versions.

test/transformer/fails_to_load_a_pubspec_with_reserved_transformer_test.dart

Index: test/transformer/fails_to_load_a_pubspec_with_reserved_transformer_test.dart
diff --git a/test/transformer/fails_to_load_a_pubspec_with_reserved_transformer_test.dart b/test/transformer/fails_to_load_a_pubspec_with_reserved_transformer_test.dart
index 4a5ecb6c5fd8cbf993f814c214dbb955e2cc8a94..65b553e9e0516bb09824d61a7c0896327d693c8c 100644
--- a/test/transformer/fails_to_load_a_pubspec_with_reserved_transformer_test.dart
+++ b/test/transformer/fails_to_load_a_pubspec_with_reserved_transformer_test.dart
@@ -12,24 +12,22 @@ import '../test_pub.dart';
 import '../serve/utils.dart';
 
 main() {
-  withBarbackVersions("any", () {
-    integration("fails to load a pubspec with reserved transformer", () {
-      d.dir(appPath, [
-        d.pubspec({
-          "name": "myapp",
-          "transformers": ["\$nonexistent"]
-        }),
-        d.dir("lib", [d.dir("src", [
-          d.file("transformer.dart", REWRITE_TRANSFORMER)
-        ])])
-      ]).create();
+  integration("fails to load a pubspec with reserved transformer", () {
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "transformers": ["\$nonexistent"]
+      }),
+      d.dir("lib", [d.dir("src", [
+        d.file("transformer.dart", REWRITE_TRANSFORMER)
+      ])])
+    ]).create();
 
-      createLockFile('myapp', pkg: ['barback']);
+    createLockFile('myapp', pkg: ['barback']);
 
-      var pub = startPubServe();
-      pub.stderr.expect(contains('Invalid transformer config: Unsupported '
-          'built-in transformer \$nonexistent.'));
-      pub.shouldExit(exit_codes.DATA);
-    });
+    var pub = startPubServe();
+    pub.stderr.expect(contains('Invalid transformer config: Unsupported '
+        'built-in transformer \$nonexistent.'));
+    pub.shouldExit(exit_codes.DATA);
   });
 }